The invention relates to a low voltage miniature electric circuit breaker equipped with a mechanism controlled by a thermomagnetic trip release, associated with an opening mechanism of a molded insulated case miniature circuit breaker, comprising:
a first thermal trip release with a bimetallic strip sensitive to overload currents, PA0 a second electromagnetic trip release for protection against short-circuit currents, comprising a control coil electromagnet, made up by helical winding of a deformable conductor having a preset rigidity, PA0 and an adjustment device of the thermal tripping threshold of the first trip release. PA0 the contact points to be multiplied and the temperature rise to be reduced; PA0 good balancing of the moving assembly to be achieved due to the symmetrical structure of the multiple contact in relation to the mid-plane of the casing.
When the bimetallic strip and the electromagnet are located on the same side in relation to the position of the moving contact, one of the ends of the coil is connected to the head of the bimetallic strip by a connecting braid. Opposite the head, the foot of the bimetallic strip is generally supported by a metal support connected to an arc guiding electrode and to the pole contact pad. The braid connects the thermal trip release and the electromagnetic trip release in series. The metal support cooperates by deformation with a thermal tripping threshold adjusting screw, so as to cause a variation of the transverse clearance of the head of the bimetallic strip with the mechanism tripping bar. Heating of the bimetallic strip is direct, as the current flow takes place along its entire length. Industrial manufacture of a thermomagnetic trip release of this kind is complicated.
The object of the invention is to improve the setting adjustment of a thermomagnetic trip release for a high-rating miniature circuit breaker, and to reduce its dimensions and manufacturing cost.